Garmin Device Shows a Different Speed/Distance Compared to Training App

Virtual Speed is the speed that is displayed in a cycling app such as the Tacx Training™ desktop app or Zwift while riding on your indoor smart trainer. Virtual speed will differ compared to the actual speed of the rear wheel on your bike or the speed displayed on your Garmin device. The difference in speed will also vary depending on the model of smart trainer that you have.

NOTE: Not all cycling applications provide Virtual Speed as a feature.

Why Do Training Apps Show Me a Different Speed and Distance?

Indoor cycling apps have their own algorithm to determine how fast and far you are going based on your power output, whether you are drafting another rider, road gradient, your rider profile, and more. Due to reading power input instead of wheel rotations, the speed and distance in your cycling app will differ from the data you see on a Garmin device. Garmin's products calculate speed and distanced based on wheel revolutions whereas other apps use the amount of power you output.

Think of the biggest hill (or mountain) that you have ever climbed and the amount of effort it took to get to the top. Many indoor trainers can simulate that experience up to a point. Each trainer will be different based on the maximum incline (E.g.: slope, gradient) percentage it can simulate.

Example:

The app you are using has you climbing a hill with a 15% incline. The Tacx® FLUX S Smart trainer can simulate up to a 10% incline. You will need to spin your rear wheel faster to equal the resistance and power output a 15% incline would require. Compare this to the person next to you using a NEO 2T Smart trainer which can simulate up to a 25% incline. Their rear wheel will be spinning slower compared to yours because the NEO 2T can simulate that 15% incline. Both of you will be exerting the same amount of energy despite each wheel turning at a different RPM. Each of you look up and see that your Garmin device is reporting a different speed. This is to be expected.